First,Rubber raw material knowledge.
Raw rubber includes natural rubber (latex,dry rubber) and synthetic rubber. The main ingredients include carbon black,sulfur, accelerator DM, zinc oxide, paraffin, calcium carbonate, antioxidant D,oil, etc. Please read the following four articles for the details.
Advantages and disadvantages of rubbermaterial
Introduction of rubber additives
List of rubber additives
The main characteristics of rubberadditives
Second,Rubber raw material inspection.
The quality of raw materials directly affectsthe quality of the rubber compound, and the quality of raw materials is animportant part of controlling product quality.
Main testing content: 1. Routine testingaccording to various levels of testing standards; 2. Testing of the effectivecontent of raw materials; 3. Testing of environmental protection items.）
Third,Rubber mastication.
The molecular weight of the raw rubber isvery high, the intermolecular force is very large, the texture is hard, and theelasticity is high, which brings great difficulties to the processing andmolding. Therefore, it is necessary to use mechanical force, heat, oxygen orsome chemical agents to transform the raw rubber from a strong and highlyelastic state to a soft and plastic state.
Forth,Rubber mixing.
In order to improve the physical-mechanicalproperties of rubber products, improve molding processing, and reduce costs,various compounding agents need to be added. Rubber mixing is the process ofuniformly dispersing various compounding agents in the rubber with the help ofthe mechanical force of the rubber mixer.
Fifth，Rubber mixing and feeding sequence。
The incorrect feeding sequence duringmixing will affect the uneven dispersion of the compounding agent, and evencause scorching and roll release. Therefore, the feeding sequence is one of theimportant factors related to the quality of the compound, so the feeding musthave a reasonable order.
The order of addition is generallydetermined according to the principle of adding the compounding agent withsmall amount, large effect and difficult to disperse first, adding thecompounding agent with large amount and easy to disperse later, adding thetemperature-sensitive compounding agent, adding the vulcanizing agent andaccelerator separately.
Therefore, when mixing at the open mill,first add raw rubber, reclaimed rubber, and masterbatch to band up. If there isa solid softener such as paraffin in the formula, add it after the rubberbanding, and then add the activator (zinc oxide, hard Fatty acid), accelerator,anti-aging agent, anti-scorching agent, etc., add carbon black and filleragain, after adding carbon black and filler, add liquid softener, if the amountof carbon black and liquid softener is large, can be added alternately, andfinally add vulcanizing agent.
If there is an ultra-fast accelerator inthe formula, it should be added together with the vulcanizing agent in thelater stage. If there is Silicon dioxide in the formula, because the surface ofSilicon dioxide is very adsorbable, hydrogen bonds are easily formed betweenthe particles, and it is difficult to disperse. It should be added before thesmall material and added in batches. For NBR, because sulfur has poorcompatibility with it and is difficult to disperse, it must be added before thesmall material, and the accelerator in the small material should be added atthe end.
Sixth,Open mill rubber mixing process.
The three stages of rubber mixing: mainlyinclude three stages:
Raw rubber is heated. The raw rubber thathas been plasticized is remelted on the machine, heated to soften, and blendedwith other polymers.
Add compounding agent. Generally, softener,stearic acid, etc. are added first, and then powder and carbon black, etc.(carbon black can also be pre-mixed with some raw rubber separately to form amasterbatch). Sulfur is generally added at the end of mixing, or after thecompound has been parked, at the second re-mixing.
Mix evenly and unload the film. After allthe ingredients have been added, continue mixing to make the mixing uniform,and then unload the film.
Seventh,Open mill and internal mixer.
The rubber mill is operated manually. Theprinciple of rubber mixing is that the rubber is repeatedly sheared in the gapbetween the rotating rollers at a higher temperature.
The mixing process of internal mixer: Thegap between the surface of the rotor of the closed rubber mixer and the wall ofthe mixing chamber varies widely with the rotation of the rotor, which producesa strong shearing effect on the rubber. The mixing effect is much greater thanthat of the open rubber mixer. Various powder compounding agents are mixed withthe rubber in the mixing chamber without flying outside, and the mixing processis controlled by automatic instruments.
What is the difference between an open milland an internal mixer?
The open mill is a double-roll mill, whichuses two rollers with different rotation speeds to generate shear force toplasticize. The operation is to continuously carry out the operation oftriangulation. The internal mixer uses the internally designed blades toproduce a regular contraction of the space during relative movement to generateshearing force.
The open mill relies on manual gluing, andeach batch is different for each compounder, and the resulting glue is notstable; the open mill has a simple structure and low cost, but it islabor-intensive, pollutes, and hurts workers. Mixing with the internal mixer isstable, efficient, and high in productivity.
The open mill has a simple structure and is easyto clean; the internal mixer has a complex structure and is not easy to clean.
The open mill is unsafe and exposed to theoutside; the internal mixer is highly safe and closed.
The open mixer dissipates heat quickly; theinternal mixer is not easy to dissipate heat.
The open mill can produce films, but theinternal mixer cannot produce films.
The open mill is cheap, and the internalmixer is more expensive, but it can be heated and vacuumed. There are alsopressurized internal mixers that can be used to process materials that aredifficult to plasticize. Low labor intensity and strong adaptability.
The difference between the open mill and internalmixer process
The process of an open mill and an internalmixer is different, and the choice of an open mill or an internal mixer isbased on the characteristics of the rubber compound.
There are many differences between openmill and internal mill. It is not just about reducing labor intensity and goodoperating conditions. If the internal mixing process is not well designed,workers would rather open the mixer for rubber mixing. , Because it is easy tooperate, it is already very skilled, and the glue produced is basically noproblem.
The rubber produced by the internal mixeris several times that of the open mill, but if the process is not welldesigned, and the rubber is scorched or unevenly dispersed. The actual laborhas been spent and wasted. The raw materials have to be re-mixed. Therefore,how to design the internal mixer's process and strictly control the temperatureis a major problem of internal mixer rubber mixing. Only reasonable utilizationcan get twice the result with half the effort.
The performance difference between therubber mixed on the open mill and the rubber mixed in the internal mixer can bevery large. This difference can also be said to be caused by mixing failure,scorching or uneven dispersion of the rubber compound caused by the unsure ofthe operation process of the internal mixer.
The mixing capacity of the open mill issmall, and various dosages are easy to add because it is open, heat dissipationis fast, and the temperature effect is not so obvious. If the temperature istoo high, you can stop the mixing for a period of time and let it cool downbefore mixing; The internal mixing machine is several times that of an openmixing machine. During the mixing process, the temperature change must bestrictly controlled, and the order of the addition of small materials must becontrolled. These will affect the uniformity and scorch of the mixing; Thetemperature of the material must be strictly controlled. The temperature in theinternal mixer is very different from the temperature of the rubber. Therefore,the relationship between this temperature must be considered when controllingthe temperature, otherwise, the rubber is easy to scorch (generally theinternal temperature of the rubber is 50 -60 degrees).
In addition, dueto the large mixing capacity, it was considered that vulcanization was finallyadded through the open mixer before, but it was later found that this was notfeasible, because the material quantity of a car internal mixer was equivalentto the several cars quantity of the open mill， andcould not be mixed vulcanization. If you use an open mixer to addvulcanization, you must divide the batch of materials from the internal mixerinto several batches of material to add, but the reality is that this is notpossible, because you can’t add the material for each batch of internal mixer.To ensure that the mixing is uniform, the recalculated composition content ofthe divided rubber compound is generally uneven and incorrect, and the addedsulfur will also be incorrect and unreasonable. Therefore, vulcanization mustalso be added through the internal mixing process, and temperature control ismore important at this time.
[Hangzhou Jinghong Chemical Materials Co.;LTD][http://www.zjjhchemical.com/en/]